Hi Midas:
In reference to your question about the gold content in gold plated cards.. Take my word, they are not worth anything as far as gold content. A couple of years ago, My son sent me some that he purchased off ebay. I tried a batch in Aqua Regia and they did not work, just junk, besides they float and the paper gums up. I aborted this project.
I then tried several in my electrolytic Cell using Glycern and Easy Flow (Sulphric Acid) . after all the trouble of knocking off the plated material, there was not enough gold to even see. The only thing of value I got out of this little project was a good lesson, dont fool with cards.
Good gold plated material is only .000007 inches thick. lesser gold plated is less than that. What it boils down to, that these items are gold flashed or colored. Just junk.
Catfish